Mathematical modeling of the stripping of combustible forest materials by explosion of a cord charge

The stripping of combustible forest materials (thin twigs and needles) by explosion of a cord charge are studied by mathematical modeling of blast-wave propagation in a forest canopy for the placement of the cord charge at different heights. The calculation results allow one to reduce the consumption of explosives in extinguishing crown forest fires. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 92–99, May–June, 2006.     

Decreasing the parameters of an air shock wave using an air-water curtain

The efficiency of using an air-water drop curtain for protection from the force and noise action of an air shock wave generated by an open explosion is studied experimentally. It is shown that the curtain generated by outburst of sprayed water after an advanced underwater explosion of a demolition cord is a reliable means of pressure decrease at the shock-wave front. The dependence of the “effective coefficient of charge-mass reduction” on the position of the curtain relative to the point of explosion, its length, time of evolution, and other conditions was studied. Zones with local pressure increase or decrease in the shock wave were found, which is explained by imposition of secondary compression and expansion waves on the shock wave. Possible physical mechanisms that ensure the protective effect are considered. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 120–130, May–June, 2000.     

Combustion and detonation characteristics of hydrazine and its methyl derivatives

The basic gas-dynamic characteristics of the detonation, instantaneous combustion (explosion) in constant volume, combustion at constant pressure, and deflagration for hydrazine, methylhydrazine, 1,1- and 1,2-dimethylhydrazine, and trimethylhydrazine in mixtures with oxygen or air that are diluted with argon at varied initial pressure and temperature values are given. The main parameters of these processes are analyzed both for the case of a gaseous propellant and for the case of a heterogeneous propellant where the propellant is a highly disperse, sprayed cloud in an oxidant medium. Calculations were performed by means of the computer code SAFETY. Calculation results are in agreement with correct experimental data. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 81–96, May–June, 2000.     

Initiation of solid explosives by mechanical impact

For some organic explosives of composition CHNO, experimental values of the critical pressure of explosion initiation are compared with the maximum possible heats of explosion, which are energetic constants of particular explosives. A correlation between these quantities is established. It is shown that an increase in the enthalpy of formation of explosive molecules is a major factor for increasing the technological and operational sensitivity. Methods for controlling the critical pressure are described. Limiting heats of explosion making impossible the practical use of particular explosives are estimated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 5, pp. 101–105, September–October, 2008.     

Secondary sites of fire in an explosion of organic dust

Formulas for the pressure, momentum, and time of impact of a shock as functions of the energy of a spherical explosion in air and the distance to the center of the explosion are used to calculate parameters of the incident and reflected (from a rigid obstacle) shock waves produced by an explosion of a concentrated mass of organic dust. The distances from the explosion center are determined within which the temperature in the incident or reflected shock waves exceeds the ignition temperature of the particles suspended in air and secondary sites of fire can be initiated by the shock passing through the dusty space. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 3, pp. 60–64, May–June, 2000.     

Initiation of chain and thermal explosions by the reactor surface. Criterion for the participation of branching chains in a thermal explosion

The combustion of hydrogen and silane is studied. It is established that the chain initiation reaction on quartz in the zone of hydrogen and silane combustion is manifested as an autocatalytic reaction which is able to initiate a chain explosion and participate in the initiation of a thermal explosion. It is shown that in the case of an oxyhydrogen gas, the assumption of a branching-chain nature of the third limit is inconsistent with Semenov’s law, which includes double exponential dependences of the chain reaction rate on time and temperature. A criterion for the participation of branching chains in complex processes is proposed based on the presence or absence of short delays of a thermal explosion (≈1 sec). According to the criterion, the explosion of an oxyhydrogen gas at atmospheric pressure with delays markedly exceeding 1 sec proceeds without the participation of branching chains and is consistently explained by the joint action of autocatalytic processes on the reactor wall and gas-phase processes. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 44–51, September–October, 2007.     

Flame propagation in hydrogen-air mixtures in a tube

The propagation of a hydrogen-air flame in a closed tube 76 mm in diameter and 2500 mm in length with and without a water film moving along the tube walls was studied experimentally and theoretically, it has been found that in a smooth-wall tube the maximum turbulization factor ranges between 10 and 30 for mixtures with the volume concentrations of hydrogen 15–30%. The presence of a moving water film on the tube walls intensifies the combustion process, which manifests itself in the essential acceleration of the detonation pressure rise. However, at the same time, the maximum explosion pressure for near-stoichiometric mixtures increases, while that for leaner compositions decreases. The results obtained are interpreted qualitatively. Balashikha. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 6, pp. 14–19, November–December, 1993.     

Deflagration in a vented vessel with internal obstacles

Experiments on deflagration in a vented vessel with a volume of 11 m³ with internal obstacles in the form of arrays of metal rods are described. Experimental and calculated curves of explosion pressure versus time are given. The effect of array parameters (rod diameter and cell size, the free cross-sectional area and the number of arrays, the spacing between arrays and their arrangement) on the explosion dynamics and turbulence factor for combustion inside the vessel are determined. Quantitative data on the turbulence factor for combustion in a vessel of large volume with obstacles in the form of a set of arrays are obtained for the first time. In some cases, they far exceed the previously obtained values for the turbulence factor. It is shown that, according to theoretical predictions, the maximum explosion pressure correlates with the ratio of the turbulence factor to the discharge coefficient rather than with the turbulence factor. A formula for the calculation of this ratio is proposed. Institute of Fire Protection, Balashikha-3 143900. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 4, pp. 31–38, July–August, 1997.     

Detonation properties of ammonium nitrate

A published equation for determining the detonation parameters of mixed explosive compositions is used to compute the detonation characteristics. When this equation was used to analyze the detonation parameters of 6ZhV ammonite, the detonation characteristics of the TNT and ammonite in this composition were taken from published data and the parameters of the ammonium nitrate were determined from the equation for the mixture. The results of large-scale experiments on a mixture of no more than 3% TNT with ammonium nitrate are presented. The detonation velocity of ammonium nitrate is found to be 5 km/sec. The equation for the mixture is used to determine the pressure and adiabatic exponent of the explosion products of ammonium nitrate when the size of the explosion exceeds the limiting diameter. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 2, pp. 102–104, March–April 1999     

Detonation of propane-air mixtures under injection of hot detonation products

The tube for spontaneous detonation (Institute of Technical Physics, Russian Federal Nuclear Center, Snezhinsk) was used to study the initiation and development of detonation in propane-air mixtures under injection of hot detonation products into them. The full picture of this phenomenon was recorded: the injection of hot detonation products into the main tube of the facility with the formation of a mixture of the starting propane-air composition with the hot products; the initiation of a local explosion in this mixture and the subsequent development of a detonation in it; detonation transfer to the region of the cold starting reactants (or detonation failure at the interface). The detonation was found to exist for an initial volume concentration of propane of 3.3 to 5%. The following critical (by the moment of the local explosion) parameters were determined: a mass fraction of hot detonation products of 6–9%, an energy input density due to product injection of 145–195 J/g, and an input energy power of 70–50 J/(g · msec). __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 3, pp. 100–109, May–June, 2006.     

Gap effect on the initiation of detonation in gas mixtures in cylindrical combustion chambers. II. Triggering of detonation within a turbulent flame

Schlieren moving-picture photography is used to study the burnup of oxygen gaseous mixtures in a cylindrical chamber with a gap at its periphery. It is found that a flame penetrating from the chamber into the gap can accelerate up to detonation speeds. The reaction wave in the gap precedes the primary combustion front propagating through the chamber and the reaction products escaping the gap create secondary combustion sources in the chamber. A process occurs in which a detonation wave that appears in the gap near one flank of the flame enters the main volume through the opposite flank, first triggering an explosion in the turbulent combustion zone (“an explosion within an explosion”) and then a detonation wave in the unreacted gas charge (“knock” in an engine). An interpretation is provided for the gas-dynamic structure of the secondary combustion source which is created in the cylindrical combustion chamber by a detonation wave propagating in the gap. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 77–87, July–August 1998     

Simulation of shock wave impact due to explosion on a flying flexible aircraft

This paper describes the results obtained by a computational simulation of the impact of shock waves due to explosion on a flying flexible aircraft of commercial type. An explicit three-dimensional dynamic nonlinear coupled analysis has been conducted by means of the software MSC.Dytran. A Lagrangian mesh has been used for the structural parts, and a Eulerian domain is used for the surrounding fluid. The fluid-dynamic solver uses a Eulerian approach and employs a finite volume method to discretize the governing equations. Structural elements are discretized by the Finite Element Method. The impact of the related shock waves on a simple panel and a wing box has been considered. The vibration of an aircraft as a whole, caused by its flexibility, has been analyzed. The analysis has mainly shown that the conducted investigation can be used to evaluate the loads on the aircraft for various initial positions of the explosion as well as for various amounts of the explosive charge. The method could permit a better design of the aircraft with respect to explosion phenomena and simulation of aircraft accidents, aimed at understanding their causes. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 121–130, November–December, 2007.     

Dynamics of phase-formation processes during self-propagating high-temperature synthesis in the thermal explosion regime

Specific features of formation of temperature and concentration fields during self-propagating high-temperature synthesis in the thermal explosion regime in a cylindrical reactor are studied by methods of mathematical modeling. The calculations are performed with allowance for melting of one (chemically active) component in the approximation with the high-melting component being non-soluble in the melt of the low-melting component. It is shown that the conditions of complete conversion of the original components in the volume of the reacting mixture depend on relations between the Biot criterion of the system, the ambient temperature, and the thermal effect of the reaction. After the thermal explosion, which occurs when the melting front reaches the geometric center of the reactor, a front of complete conversion is formed. This front moves from the cylinder centerline to the periphery with a gradually decreasing velocity. The diagram of the critical values of the Biot criterion at which the components burn down completely in the entire reaction volume is calculated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 31–38, July–August, 2008.     

Explosive characteristics of aluminized HMX-based nanocomposites

The explosive characteristics of HMX compositions doped with 15% Al (by weight) were studied experimentally. The detonation velocity, pressure and temperature profiles, the velocity of endwise acceleration of plates, and the heat of explosion of dense pressed samples were measured. The results were compared for compositions based on mechanical mixtures of initial micron-size particles of HMX with aluminum powders of various sizes and for nanocomposites. The addition of nanoaluminum reduces the detonation velocity to a greater degree than the addition of micron-size aluminum. The mechanical mixtures have close detonation velocities, whereas in composites containing different types of nanoaluminum, they differ by almost 200 m/sec. For all compositions, except for the most homogeneous nanocomposite, two-peak pressure profiles are observed. For charges of a composite and a mechanical mixture with nanoaluminum of the same type, the second peak pressures almost coincide but are reached in different times. At the same time, the peak pressure increases with decreasing aluminum particle size. The temperature profiles agree qualitatively with the pressure profiles. The velocity of endwise acceleration of plates depends linearly on the activity of the aluminum powder used. Nanocomposites and mechanical mixtures containing the same aluminum powder have close heats of explosion. Nanoaluminum is almost completely oxidized during calorimeter bomb tests, and the major factor determining the heat of explosion of the compositions with nanoaluminum is also the content of active metal in the aluminum powder. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 85–100, March–April, 2008.     

Hypothesis on the nature of the Tunguska meterorite

It is shown that all the specific features of the Tunguska catastrophe in 1908 can be explained by an explosion of a methane-air cloud which was initiated by a stony or iron meteorite whose mass was of the order of several tens of tons. The meteorite gently flied at an altitude of several kilometers with a velocity of 1–2 km/sec. A single ejection of 200 ktons of methane into the atmosphere is sufficient to form such a cloud. The meteorite fell several tens of kilometers from the epicenter of the explosion. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 120–122, January–February, 1998.     

Effectiveness of combustion of shock-dispersed fuels in calorimeters of various volumes

The combustion of a shock-dispersed-fuel charge consisting of 1-g flake Al in 6.6-, 21.5-, and 40.5-liter bomb calorimeters were investigated. Wall pressure histories were used to diagnose the effect of energy release due to turbulent mixing and combustion of the explosion cloud with air. These effects lead to a factor of four increase in the peak quasistatic pressure for the 6.6-liter chamber. Pressure decay was observed at late times and was ascribed to energy losses to the walls due to radiation heat transfer. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 121–125, November–December, 2006.     

Motion of a shaped-charge jet in a porous medium

The problem of the motion of a shaped-charge jet in a porous medium is equivalent to the problem of a blunt cylinder in a hypersonic flow whose velocity at infinity is equal to the jet velocity in the porous medium. The flow pattern of the medium is the same as in the case of propagation of a blast wave generated by a point explosion of a cylindrical charge. The approximate theory of a strong explosion is used to obtain the basic relations for the shock wave and the expanding cavity in the hypersonic flow of a porous medium around the blunt cylinder. A comparison with experiments on the motion of a copper shaped-charge jet in porous aluminum is performed. Translated fromFizika Goreniya i Vzryva, Vol. 35, No. 6, pp. 119–124, November–December 1999.     

Hydrodynamic effect of an electrical explosion on the ignition of condensed materials

The ignition of condensed materials by an electrical explosion is studied numerically. The effect of the wave process in the sample on its ignition characteristics is analyzed. Calculated values of the ignition time are given for various sample layouts, sample dimensions, and parameters of the initiating pulse. The effect of the hydrodynamic process caused by an electrical explosion in a condensed reactive material on the ignition period is studied. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 15–22, January–February, 2007.     

Heat of explosion of commercial and brisant high explosives

Methods for determining the heat of explosion of high explosives (HEs) with ideal and nonideal processes of explosive decomposition are considered. It is shown that the heat of explosion is of significance for estimating the efficiency of commercial HEs and is used in the energetic characterization of the working capacity. The heat of explosion of brisant HEs is only part of the blast heat of explosion and is the heat content of gaseous detonation products during their isentropic expansion from the initial state to a certain expansion ratio (determined by experimental conditions). The heat of explosion can be obtained by thermodynamic calculations based on physically justified equations of state for fluids (gaseous detonation products in the chemical-reaction zone of the detonation wave in the supercritical state) and condensed nanocarbon phases (nanographite, nanodiamond, and liquid carbon). Experimental and calculated values of the heat of explosion are given. The thermodynamic calculation is inapplicable to commercial HEs because of the nonideal nature of their detonation. The heat of explosion of commercial HEs can be calculated using the Hess law. The heat of explosion of brisant HEs is not a measure of power. The power of HEs is characterized by the propellant performance. It is shown that even detonation velocity cannot be a measure of the power of HEs. The power and detonation parameters of brisant HEs are determined by the energy release density in unit volume of the chemical-reaction zone of the detonation wave and by the rate of energy release from the shock front rather than by the heat of explosion, which cannot be considered a universal characteristic. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 2, pp. 100–107, March–April, 2007.